The instant invention relates to washing apparatus and, in particular, to dispensers for dispensing a preselected quantity of liquid additive at a preselected time into washing liquid during a washing operation.
Conventional dishwashers effect cleaning by means of a preselected timed sequence of wash and rinse cycles in which different additives are introduced to the dishwashing chamber. Thus, detergent may be dispensed at different times during the wash cycle and rinse additives to provide improved rinsing of the washed dishes may be dispensed during the rinse cycle. Automatic dispensers which operate in preselected time sequence have been provided in the past to effect the dispensing operation. However, because of the conditions under which such dispensers operate, it is desirable to provide such dispensers with a minimum number of moving parts along with substantially clog-free construction. Likewise, for competitive reasons it is desirable to provide such dispensing structures which are extremely simple and economical in construction while still providing positive dispensing with minimum maintenance over long periods of use of the apparatus and elimination of any possibility of leakage.
One dispenser for a water conditioner for use in a dishwasher is shown and described in U.S. Pat. No. 3,029,826 of Donald E. Fink et al. In this dispenser a measuring cup is filled with a preselected quantity of liquid additive on opening and closing of the dishwasher door. The liquid additive is then discharged at the appropriate time in the dishwashing cycle by opening a valve to allow the liquid additive to flow by gravity from the measuring cup into an exit port and thence into the washing chamber of the dishwasher. This particular structure has the disadvantage of requiring many moving parts and particularly, moving parts in a valve system which ultimately result in wear and thus leakage of the liquid additive into the washing chamber prior to the time required in the preselected wash cycle. For example, a rinse additive could thus leak into the washing chamber during the wash cycle and be discharged from the dishwasher prior to the rinse cycle even beginning.
Still another automatic dispenser for a dishwasher is described in U.S. Pat. No. 3,828,975 of William F. Robandt, II et al. The dispenser disclosed in this patent is arranged to supply a quantity of liquid additive as an incident of moving the dishwasher door between opened and closed positions and to dispense the quantity subsequently at the desired time in the dishwashing cycle. The quantity of liquid additive is not truly preselected as the quantity supplied to the measuring means varies with the quantity of liquid additive in the reservoir. This roughly measured quantity of liquid additive is then discharged by a pressure producing means into the washing chamber. While this construction eliminates premature leakage of liquid additive into the washing chamber, it does not precisely measure a preselected quantity of additive and thus of necessity is wasteful in that it must supply a minimum quantity of additive sufficient to effect the desired result when the additive reservoir is nearly empty and therefore, due to the design, supplies an excess of additive when the additive reservoir contains more than the minimum quantity of additive to be operable. Furthermore, leakage from the washing chamber into the measuring chamber could also result in dilution of the liquid additive thereby resulting in a further wasteful oversupply of liquid additive to the washing machine chamber on that cycle and possibly diluting the liquid additive during subsequent wash loads so as to result in insufficient additive being supplied when the additive level in the reservoir approaches its minimum.